Method and installation for separating constituents of used tires

ABSTRACT

The invention concerns a method for treating tyres, belts, inflatable boats, boots and other manufactured articles containing rubber, polymers and reinforcing elements, which is a close circuit system consisting in immersing the waste materials to be treated in a hot alkaline hydroxide bath, followed by neutralization of the resulting materials with a weak mineral acid solution for industrial re-use of said materials.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Stage of International ApplicationNo. PCT/BE98/00180 filed 20 Nov. 1998, and Belgian Application No.9700933 filed 20 Nov. 1997. The entirety of each of those applicationsis incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a process and a plant for the treatmentof vulcanized rubber of all kinds, such as tyres, conveyor belts, boots,shoes and other objects containing assembled rubber and polymermaterials for the purpose of recycling the components by the relevantindustries.

The bulk of these materials is represented above all by the increase inroad transport development which gives rise to worrysome quantities ofdowngraded tyres difficult to remove and possibly to recycle.

It should not be forgotten that more than 3 billion tyres, merely fromprivate vehicles, are running along the roads in the various countriesand, of course, have to be periodically replaced. In terms of weight,this represents at least 18 million tonnes of bulky waste which has tobe disposed of, something which represents a serious ecological problemdifficult to solve, and above all since people are becoming increasinglyaware of environmental problems and regulations.

A vast quantity of tyres is destroyed by incineration and in cementkilns with recovery of thermal energy. This approach is beingincreasingly questioned because of the atmospheric pollution and of thedestruction of materials which are beneficial to recover.

Another process consists of successive grinding so as to end up withsmall particles that can be used as fillers in bitumens and asphalts.Such grinding has been facilitated by cryogenic techniques. However,multiple shredders, which are indispensable for shearing the metalreinforcements, in order to produce reusable powder, are heavy machineswhich devour energy and are consequently very expensive.

Another destruction process, with recovery of certain components, isbased on pyrolysis. The recycling consists in recovering the pyrolysisoil, the carbon and the metals. These processes are high-performanceprocesses but they require the investment of large sums of money andhigh treatment costs, they are often the source of significantatmospheric pollution.

Thus efforts have been intensified to develop methods for stripping thisbulky waste in a manner which is effective, economical andenvironmentally non-polluting. Considerable research has been focused onthe problem, which obviously does not concern only worn tyres but allmanufactured products made of rubber and also the waste accompanying themanufacture of these products, these often being reinforced with metalreinforcements or reinforcements made of synthetic materials. Theultimate problem does not reside only in the economical destruction ofthe rubber element or of the tyres, but it is also desirable to be ableto recover and reuse them, or some of the components, for the purpose ofavoiding unnecessary wastage of beneficial materials.

With the aim of illustrating the prior art in this field, it isappropriate to mention the following publications:

-   -   GB 2,026,144 (1979) discloses a plant for the treatment of        rubber waste and of synthetic materials coming from worn tyres.        Thermal decomposition of the product, which is coarsely reduced,        is carried out in a fluidized bed of sand at 800° C. in the        presence of oxygen. The gases produced by the decomposition are        used and, at the end of the process, the reinforcing metals are        recovered by means of magnets.    -   U.S. Pat. No. 4,426,459 (prior. JP 1980) discloses a process for        the decomposition of vulcanized rubber by a treatment around        100° C. with an organic solvent in the presence of an alkaline        hydroxide such as potassium hydroxide.    -   DE 3,313,470 (1983) relates to a method and to an apparatus for        treatment at a temperature above 200° C. for 10 to 35 minutes in        a liquid phase composed of spent mineral oils and of organic        solvents. A viscous product is obtained which can be used as an        additive in bitumens or insulation layers.    -   WO 97/1561 (prior. U.S. 1995 and 1996) describes a process for        the devulcanization of rubber coming from downgraded tyres by        desulphurization at around 300° C. by means of an alkali metal        in a medium that does not contain oxygen, before or during a        treatment by an organic solvent after having separated the        constituents of the tyres, such as the steel and other        reinforcements.

Many of these processes have disadvantages, namely from the standpointof the investments, of the efficiency, of the complexity, of theenvironment or of the market.

SUMMARY OF THE INVENTION

The object of the present invention is to remedy these drawbacks and topropose a process and a simple plant allowing separation of vulcanizedand/or bonded rubber waste, such as tyres, belts or other objects, andallowing the constituents to be recovered for reuse by industry, withoutendangering the environment. The separation of the rubbers from theother materials and metal or other reinforcements is easilyaccomplished, quickly and economically, the reinforcements made ofsynthetic resins being dissolved and the metal recovered. Thus, it ispossible to provide industry with quality products at competitiveprices.

The process essentially comprises the following steps:

-   A) The reinforced or non-reinforced, vulcanized-rubber waste is    coarsely reduced by cutting it up by means of a saw, preferably of    the guillotine type fitted with cutters in a grating in order to    obtain fragments 10 to 25 cm in length. The sole purpose of this is    to reduce the size and thus facilitate handling during the treatment    process.-   B) The reduced waste is introduced into a reactor and treated for 30    minutes at 350° C. with an OH⁻ ion generator, preferably a strong    alkaline base such as molten NaOH. 3. Separation of the basic liquid    and the residues coming from the treated rubber.-   C) Neutralization of the residues with an acid, such as phosphoric    acid;-   D) Recovery and separation of the rubber constituents and the metals    used for reinforcement.

Destruction of some of the bonds between the rubber and the otherreinforcing materials is achieved by the action of a strong alkalinebase, such as molten NaOH which is maintained at a temperature of 350°C. for approximately 30 minutes.

It is important to point out that the consumption of basic agent is verylow and the etching liquid can be reused several times, by recovery andreinjection; the volume of the NaOH liquid product circulating will beautomatically readjusted if necessary by a fresh addition of theproduct. Moreover, it should be emphasized that the process according tothe present invention does not involve any organic solvent. In addition,it works with waste which is only coarsely cut up and the substancesserving for the proposed treatment are well known, commonly employed andinexpensive.

The plant for implementing the process is relatively simple and does notentail inordinate investment.

BRIEF DESCRIPTION OF THE DRAWINGS

The details of the process according to the present invention willemerge from the description of the plant which relates thereto, thedescription being given by way of non-limiting example.

FIG. 1 shows schematically the overall plant;

FIG. 2 shows, on a larger scale, the first part of one of the possibleembodiments of the plant;

FIG. 3 shows, on a larger scale, the second part of one of the possibleembodiments of the plant.

DETAILED DESCRIPTION

As shown in FIG. 1, crystallized NaOH in its original package is meltedin the oven 1, at a temperature of 300 to 400° C., before beingintroduced into the master tank 5, which is provided with a heater andin which the NaOH is maintained at a temperature of 380° before beingtransferred to the reactor 13 into which the waste coming from thecropper 14 is also introduced. After 30 minutes of immersion and withstirring at the start of obtaining a temperature of 350° C., the liquidis conducted by the line 19, provided with a pump, to the buffer tank 20and then sent to the master tank 5. The buffer tank is heated to atemperature of 380° C. in order to prevent heat shocks occurring in thetank 5. Moreover, the buffer tank is designed to gather the precipitatesand is organized for the separation and extraction of the smallparticles. The decomposition products from the reactor 13 aretransferred to the neutralization tank 23 and, at the end of thetreatment, the residues are transported to the magnetic sorting device32 where the metals are separated from the polymers resulting from thetreatment.

According to this embodiment illustrated in greater detail in FIGS. 2and 3, a drum 0 containing crystallized NaOH is introduced into the oven1, which matches the shape of the drum, in which oven the NaOH is heatedto a temperature of at least 380° C. The upper part and the straightvertical part of the oven form a cover which opens about the spindle 2fastened to the bottom right of the oven in order to allow the drum tobe easily loaded. A connection tube running to the pump 3 is introducedand connected to the bung of the drum.

The liquified NaOH is transferred to the master tank 5 in which it ismaintained at 350° C.

The master tank 5 is equipped with conventional monitoring and controlinstruments 8 to 11, known to those skilled in the art, which monitorthe conditions in the tank and actuate the electronic control actuatorswhen transfers are made and when other actions are taken. The regulatorysafety valve 7 prevents unexpected and accidental overpressures and theheating element 6 (which may be placed on the outside, between theinsulation, by heating coils conveying a warm liquid) keeps thetemperature constant inside the tank.

The liquid is sent via the line 12, fitted with a pump, into the reactor13 and the waste, cut up in the cropper 14, advantageously a guillotine,is sent by the chain conveyor 15 into the reactor 13, the solidmaterials must be immersed, the amount of caustic liquid is attained bythe operation and control of a probe which also actuates the closure ofthe valve 17 and the start of the stirring provided by the mixer 16. Thetemperature of the reactor is maintained by the heating system 18. Afterapproximately 30 minutes treatment at 350° C., the materials aredeconsolidated, the caustic liquid is extracted by the line 19, fittedwith a pump, through a filter 21, to the buffer tank 20. The filter 21retains the particles greater than 1 mm. It is unclogged suddenly byclosing the valve of the line 19 and sending compressed air 44 into thatpart of the line 19 which is connected to the tank 13.

The buffer tank 20 is equipped with the same monitoring, control andheating apparatuses as the tank 5; it has a configuration which allowssettling and reheating of the caustic liquid to the temperature of 350°C. in order to avoid thermal shocks and the risk of crystallization inthe master tank 5. The liquid in the decanted part and at the correcttemperature in the buffer tank 20 is then sent back via the line 21, bygravity, slowly into the master tank 5.

When all the caustic liquid has been withdrawn from the reactor 13, thelarge valve 22 is opened and releases, by gravity, the materials in thereactor 13 into the neutralizing tank 23.

The neutralizing liquids for the above treatments and for cleaning theplant, coming from the tank 24, are conveyed by the line 25, fitted witha pump, to the neutralizing tank 23 into which the liquid is injected bysprayheads. The phosphoric acid coming from the tank 26 passes via themixing unit 27 through the line 25. The materials and the liquid arevigorously stirred. The pH meter 11 sets the pH=7 after a little morestirring, there is a hold period in order to allow the suspendedmaterials to precipitate, the neutralized liquid is extracted just atthe point of connection of the line 28, fitted with a pump, to the tank23. Injections of air 44 into this line have the purpose of clogging thefilter installed at the end of the line 28.

The neutralized liquid having been withdrawn, the large valve 29 isopened while the valve 30 remains closed. The neutralized liquid isfound in the tube with the materials between the two valves 29 and 30,it is withdrawn through the bypass of the line 28, the bypass also beingequipped at the end of the line with a filter unclogged by suddeninjections of air 44, and then the liquid is directed into the tank 24.After removing the rest of the liquid, the valve 30 is gradually openedso as to release the solid material coming from the neutralizing tank23.

The material is transported by a conveyor belt to the magnetic pulley 32located at the end of the belt. The metals 33 are precipitated into thecontainer 34 and the non-magnetic materials 35 end up in the container36. The container 36 is provided with a double bottom, the materialbeing deposited on the first bottom provided with a stainless steelfilter whose porosity is less than 10 microns. The material is dried byliquid flow via a lateral pipe 45. The containers 34 and 36 aresuperposable and have opening bottoms.

Liquified NaOH has a boiling point greater than 1000° C.; there is nopressure formation in the plant, however the equipment is designed towithstand a pressure of 10 bar in anticipation of possible heat shocks.

As this is a heat treatment, it is preferable to work continuously aslong as possible. For this purpose, and in order to avoid shut downs dueto the build-up of impurities and small particles, cleaning devices areprovided for removing them, without having to stop the production. Aftera number of treatments and in anticipation of cleaning the buffer tank20, the NaOH liquid in the master tank 5 will be taken to the minimumlevel in order to receive the entire solution stored in the buffer tank20, up to the level of the tap on the line 21. Next, water will beslowly added via the line 37 to the rest of NaOH liquid, bottom of thebuffer tank 20 for a direct dilution to the point of non-crystallization(concentration +/−40%). After this dilution, the valve 38 is opened on avibrating screen 39 having a porosity of 10 microns. The solid particlesare removed to a container 40 and will be able to be transferredthereafter to a washing tank external to the system with a filter pressfor the impurities precipitated by the neutralization and for recoveringthe materials to be recycled in a container of the 36 type. The 40% NaOHsolution is recovered via the outlet 41. It will be put into drums andsold for another use or else introduced into the tank 24 in order toobtain a neutralizing agent and thus increase the profitability of theprocess.

Cleaning during production of the storage tank 24 is also provided. Thistank having fed the neutralizing tank 23, the surplus neutral liquidwill be withdrawn up to the level of the tap of the line 42 in order tobe put on standby in the neutralizing tank 23. This will be organizedduring the time for a treatment of the reactor 13 and for theneutralization which occupies the liquid. Provision shall be made forthe tank 24 to be cleaned and for the liquid in the tank 23 to bereturned to 24 during this reaction and neutralizing time.

When the lower level corresponding to the tap of the outlet 42 isreached, the valve 43 opens and releases the particle-laden neutralliquid onto a vibrating screen identical to 39. The liquid is removedand the particles recovered.

During temporary shut-down or shut-down of short duration of the plant,the heating of the master tank 5 and possibly buffer tank must not becut off. For a complete shut-down, it will be essential to drain, whilehot, the buffer tank 20 to the master tank 5 and then via the line 43,connected to a battery of drums in which the solution will crystallize.To reuse the NaOH, the drums will be placed in the oven 1.

For the neutralization, the process makes use of acids, preferablyphosphoric acids for the neutralization. It is quite conceivable to usematerials such as phosphoric acid solutions regarded as waste in theindustry—this waste is available in large quantity. The process acceptsvarious concentrations, even low concentrations, the adjustment is doneautomatically. Consequently, the system may be regarded as aneutralization centre for these acids, constituting an appreciablefinancial plus, thus reducing the cost of the main treatment forming thesubject of the present invention.

The recovered metals will be sent to the steel industry.

The other materials recovered from the tyres are friable and areconverted into a fine powder with slight pressure. Devulcanization isnot complete but the breaking of certain bonds is ensured. The friablenature and the polymeric composition of the residue make thereof abeneficial filler material, to be recycled in the manufacture of tyresand rubber articles, and for other non-limiting applications, such as inbitumens or other bitumenous mixes.

It is obvious that the present invention is in no way limited to theembodiment as described in the illustrative embodiment shown in FIGS. 1,2 and 3. Variants may be made to it without thereby departing from thescope of the claims.

1. A plant for implementing a process for treating vulcanized-rubberwaste, wherein the process for treating vulcanized-rubber waste includesthe steps of: coarse cutting of said waste into fragments, attackingsaid fragments using a molten pure base under temperature conditionscausing, in the presence of molten pure cast NaOH as the molten purebase, deconsolidation of the vulcanized rubber waste into deconsolidatedsolid fragments of polymeric composition: separating said molten basefrom said deconsolidated solid fragments; neutralizing saiddeconsolidated solid fragments; and recycling or reutilizing theneutralized, deconsolidated solid fragments wherein the plant forms acompletely closed system, with no atmospheric pollution, the plantcomprising: a device for melting said molten pure base; a reactorconnected to said melting device, into which said vulcanized- rubberwaste, which has been coarsely cut into pieces, and said molten purebase are introduced, and in which reactor temperature conditions areapplied causing deconsolidation of the vulcanized-rubber waste intosolid fragments of polymeric composition; a separating device connectedto an outlet of said reactor and allowing the molten base to beseparated from the deconsolidated solid fragments; a neutralizing devicefed with neutralizing agent from a source of neutralizing agent, inwhich device the deconsolidated solid fragments are neutralized; and adevice connected to the neutralizing device for sorting the neutralized,deconsolidated solid fragments.
 2. The plant according to claim 1,wherein said separating comprises sedimentation of the deconsolidatedfragments, separated beforehand from the molten base, in a settling andneutralizing liquid, and, after removal of the settling and neutralizingliquid, recovery of the deconsolidated fragments.
 3. The plant accordingto claim 1, further comprising a device for recycling of the molten purebase.
 4. The plant according to claim 1, that wherein the molten NaOHtreatment temperature is at most 400° C.
 5. The plant according to claim1, wherein the deconsolidated solid fragments comprise metal fragmentsand fragments made of synthetic material and wherein the processfurthermore includes sorting between the metallic and syntheticdeconsolidated fragments before they are recycled or reutilized.
 6. Theplant according to claim 1, wherein the deconsolidation takes place in aclosed reactor, the waste to be treated being completely immersed. 7.The plant according to claim 1, wherein the neutralizing uses at leastone dilute acid.
 8. The plant according to claim 1, wherein the reactorhas closeable inlet and outlet openings, stirring equipment, and whereinsaid separating device comprises a filter capable of retaining particlesgreater than 1 mm inside the reactor.
 9. The plant according to claim 1,wherein the neutralizing device comprises: a tank provided with an inletcommunicating with an outlet of the reactor; and with an outlet; theinlet and outlet being closeable; stirring equipment; and a filter in anoutput line.
 10. The plant according to claim 1, wherein theneutralizing device comprises a tank for injection of neutralized liquidand for recovery.
 11. The plant according to claim 1, wherein theneutralizing device comprises another tank which contains acid waste andis connected to a mixing unit.
 12. The plant according to claim 1,further comprising devices for cleaning precipitates and small particlesin the NaOH.
 13. The plant according to claim 1, wherein the device forsorting comprises a device for transporting the deconsolidated materialswith magnetic separation of metallic materials.
 14. The plant accordingto claim 1, wherein the vulcanized rubber waste consists of one or moreof tyres, boots, inflatable boats and reinforced rubber articles. 15.The plant according to claim 4, wherein the molten NaOH treatmenttemperature is at most 350° C.
 16. The plant according to claim 7,wherein the at least one dilute acid is phosphoric acid.
 17. A processfor treating vulcanized rubber waste, comprising the steps of: coarsecutting of the vulcanized rubber waste into fragments, attacking thefragments using a molten pure base under temperature conditions causing,in the presence of molten pure cast NaOH as the molten pure base,deconsolidation of the vulcanized rubber waste into deconsolidated solidfragments of polymeric composition; separating the molten base from thedeconsolidated solid fragments; neutralizing the deconsolidated solidfragments; recycling or reutilizing the neutralized, deconsolidatedsolid fragments; and wherein the neutralizing uses phosphoric acid. 18.The process according to claim 17, wherein said separating comprisessedimentation of the deconsolidated fragments, separated beforehand fromthe molten base, in a settling and neutralizing liquid, and, afterremoval of the settling and neutralizing liquid, recovery of thedeconsolidated fragments.
 19. The process according to claim 17, furthercomprising the step of recycling the molten pure base.
 20. The processaccording to claim 17, wherein the molten NaOH treatment temperature isat most 400° C.
 21. The process according to claim 17, wherein thedeconsolidated solid fragments comprise metal fragments and fragmentsmade of synthetic material and wherein the process furthermore includessorting between the metallic and synthetic deconsolidated fragmentsbefore they are recycled or reutilized.
 22. The process according toclaim 17, wherein the deconsolidation takes place in a closed reactor,the waste to be treated being completely immersed.
 23. The processaccording to claim 17, wherein the vulcanized rubber waste consists ofone or more of tyres, boots, inflatable boats and reinforced rubberarticles.
 24. The process according to claim 17, wherein the molten NaOHtreatment temperature is at most 350° C.